The subject matter of this invention relates generally to programmable controllers, and more specifically to contact interconnection indicia on the programming panel thereof and the cooperation of the controller memory and line solver of the controller with the programming panel.
Relay logic ladders include rungs of interconnected switches, relay contacts and output devices (such as relay coils) disposed in rows between two conductors of a power supply. The ladders work by using the principles of relay logic for controlling electromechanical devices. According to art which predates the advent of relay line solver technology, relays, switches and other devices of the logic ladders (which are hard-wired, relatively large electromechanical devices) are strung together between the conductors of a power supply. The various switches and contacts of the relay logic ladder are in various states of conduction or non-conduction depending upon the disposition of mechanical devices, such as floats, or depending upon the disposition of output devices, such as relay coils, to which they are interlinked electrically or mechanically. In the event that appropriate contacts or switches are in a closed state in a given rung of the ladder, the output device, usually a relay coil, controlled by the rung will be actuated. The actuation may cause certain phenomena external or internal to the relay ladder to occur.
With the advent of computer technology, the relay ladder diagram, which is a graphical representation of the relay ladder, is simulated within a programmable controller. This eliminates the bulky, relatively expensive relays, saves space, and generally reduces the need for expensive hard-wired interconnections. The programmable portion of the controller gives the controller operator or logic system designer flexibility. According to still other art, the various interconnections between contacts, switches and output devices in a relay rung are simulated with a diode matrix, as is taught in U.S. Pat. No. 3,950,736, issued Apr. 13, 1976 to Dix et al. Essentially, this requires the use of a diode matrix which can be programmed by moving diodes into and out of the matrix in a predetermined fashion. One disadvantage of this is the relatively cumbersome arrangement of the diode matrix and the level of dexterity and skill required in using or programming it. In still other art concerned with a computer controlled ladder diagram solver (sometimes called a line solver), a programming panel is used for initially programming or for subsequently changing the status of various memories contained therein.
As the latter prior art developed, it is suggested that certain characteristics began to emerge as important. They are: complexity of the problem to be solved; memory efficiency; and operator skill. Complexity of the problem to be solved is associated primarily with the arrangement of the interconnections between elements in a rung of a ladder diagram and, to a lesser extent, with the number of elements in a rung of a ladder diagram. Memory efficiency is associated with the number of memory bits or locations required for complete entry of a rung of a ladder diagram into the programmable line solver. Operator skill is associated with the operator's capability for converting the symbols of a rung of a ladder into manipulations of the programming panel (a program loader) of the programmable controller with maximized speed and minimized potential for error. An examination of the prior art shows that the attainment of all three important features in a single programmable controller is difficult. Consequently, the prior art seems to branch in two directions--the choice of which depends upon which of the aforementioned important functions is to be optimized at the expense of the others. In one case, optimization tends towards flexibility--that is, the programmable controller is designed and constructed so that relatively complex ladder diagrams can be entered into the programmable controller for solution thereby at the expense of memory efficiency. One of the problems associated with memory lies in the fact that in most of the prior art of the aforementioned kind, separate memory words must be utilized for entering the elements and for entering the interconnections between elements in a complex ladder diagram. Corollary to this, is that additional operator manipulations of the programming panel be all made by the operator to place the additional interconnection information into the memory. Examples of the preceding may be found in U.S. Pat. No. 4,021,783, issued May 3, 1977 to G. C. Highberger and entitled "PROGRAMMABLE CONTROLLER". A further example is found in the Allen-Bradley Company Bulletin No. 1774, entitled "PLC PROGRAMMING AND OPERATION". Still a further example is found in a bulletin from Industrial Solid State Controls, Inc. dated January 1973 entitled "IPC.TM. INDUSTRIAL PROGRAMMABLE CONTROLLER MEMORY LOADER/MONITOR (L/M)". Still another example is found in U.S. Pat. No. 3,686,639 issued Aug. 26, 1972 to Fletcher et al and entitled "DIGITAL COMPUTER-INDUSTRIAL CONTROLLER SYSTEM AND APPARATUS". Another example is found in a SQUARE D COMPANY bulletin dated Jan. 2, 1975, identified by the following: "Cl.8881 PROGRAMMABLE CONTROLLER PROGRAM BOX--APPLICATION OF TYPE PR-2 PROGRAM BOX". Another example is found in apparatus described in a manual provided by the MODICON Company, entitled, "MODICON 184/384 MANUAL" June 1977 (for example pp 31-65 and A-2 through A-5). In the other case, the trend appears to be towards memory efficiency at the expense of flexibility. This type of controller or processor tends to be limited as to the number of elements (contacts, timers, etc.) which can be entered, the number of possible circuit combinations which can be utilized and/or the total length or size of the ladder rung. Furthermore, apparatus has been found in which some contact and associated interconnection information may be entered into one word of memory in a limited case with one key manipulation of a single key of the program panel. Such may be found in a General Electric Company descriptive bulletin dated January 1977, entitled "LOGITROL CONTROL". However, in no case discovered can an entire ladder diagram rung be entered in this way i.e. with all types of interconnections entered by use of a contact entry device or key. It would be advantageous, therefore, if a programmable controller could be found which was suitable for solving relatively complex ladder diagrams, but which nevertheless utilized a minimum number of a memory locations for storing the ladder diagram therein and which required a relatively low level of operator skill.